kolbintro5e

Chapter Introduction

CHAPTER 11

How Does the Nervous System Respond to Stimulation and Produce Movement?

355

RESEARCH FOCUS 11-1 NEUROPROSTHETICS

11-1 A HIERARCHY OF MOVEMENT CONTROL

THE BASICS RELATING THE SOMATOSENSORY AND MOTOR SYSTEMS

FOREBRAIN: INITIATING MOVEMENT

EXPERIMENTAL EVIDENCE FOR A MOVEMENT HIERARCHY

BRAINSTEM: SPECIES-TYPICAL MOVEMENT

EXPERIMENT 11-1 QUESTION: WHAT ARE THE EFFECTS OF BRAINSTEM STIMULATION UNDER DIFFERENT CONDITIONS?

CLINICAL FOCUS 11-2 CEREBRAL PALSY

SPINAL CORD: EXECUTING MOVEMENT

CLINICAL FOCUS 11-3 SPINAL CORD INJURY

11-2 MOTOR SYSTEM ORGANIZATION

MOTOR CORTEX

MOTOR CORTEX AND SKILLED MOVEMENT

EXPERIMENT 11-2 QUESTION: HOW DOES THE MOTOR CORTEX TAKE PART IN THE CONTROL OF MOVEMENT?

PLASTICITY IN THE MOTOR CORTEX

EXPERIMENT 11-3 QUESTION: WHAT IS THE EFFECT OF REHABILITATION ON THE CORTICAL REPRESENTATION OF THE FORELIMB AFTER BRAIN DAMAGE?

CORTICOSPINAL TRACTS

MOTOR NEURONS

CONTROL OF MUSCLES

11-3 BASAL GANGLIA, CEREBELLUM, AND MOVEMENT

BASAL GANGLIA AND THE FORCE OF MOVEMENT

CLINICAL FOCUS 11-4 TOURETTE SYNDROME

CEREBELLUM AND MOVEMENT SKILL

EXPERIMENT 11-4 QUESTION: DOES THE CEREBELLUM HELP TO MAKE ADJUSTMENTS REQUIRED TO KEEP MOVEMENTS ACCURATE?

11-4 SOMATOSENSORY SYSTEM RECEPTORS AND PATHWAYS

SOMATOSENSORY RECEPTORS AND PERCEPTION

POSTERIOR ROOT GANGLION NEURONS

SOMATOSENSORY PATHWAYS TO THE BRAIN

SPINAL REFLEXES

FEELING AND TREATING PAIN

RESEARCH FOCUS 11-5 PHANTOM LIMB PAIN

VESTIBULAR SYSTEM AND BALANCE

11-5 EXPLORING THE SOMATOSENSORY CORTEX

SOMATOSENSORY HOMUNCULUS

RESEARCH FOCUS 11-6 TICKLING

EFFECTS OF SOMATOSENSORY CORTEX DAMAGE

SOMATOSENSORY CORTEX AND COMPLEX MOVEMENT

Katherine Streeter

RESEARCH FOCUS 11-1

Neuroprosthetics

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Most of us seamlessly control the approximately 650 muscles that move our bodies. But if the motor neurons that control those muscles no longer connect to them, as happens in amyotrophic lateral sclerosis (ALS, or Lou Gehrig disease), movement, and eventually breathing, become impossible.

This happened to Scott Mackler, a neuroscientist and marathon runner, in his late 30s. Dependent on a respirator to breathe, he developed locked-in syndrome: Mackler lost virtually all ability to communicate.

ALS has no cure, and death often occurs within 5 years of diagnosis. Yet Scott Mackler beat the odds: he survived for 17 years before he died in 2013 at age 55. Mackler beat locked-in syndrome too, by learning to translate his mental activity into movement. He returned to work at the University of Pennsylvania, stayed in touch with family and friends, and even gave an interview to CBS’s 60 Minutes in 2008.

Mackler was a pioneer in brain–computer interface (BCI) technology. BCIs employ the brain’s electrical signals to direct computer-controlled devices. BCIs are one area of neuroprosthetics, development of computer-assisted devices to replace lost biological function.

A computer–brain interface (CBI) employs electrical signals from a computer to instruct the brain. Cochlear implants that deliver sound-related signals to the inner ear to allow hearing are CBIs. Brain–computer–brain interfaces (BCBIs) combine the BCI and CBI approaches. BCBIs enable the brain to command robotic devices that provide it sensory feedback.

In 2008, Mackler’s BCI took up to 20 s to execute a single command. Today’s devices enhance processing speed and increase signal precision by using electrodes placed directly adjacent to brain cells in arrays that interface with thousands of cells. Experimental approaches use optogenetics, incorporating light-sensitive channels into cortical motor and sensory neurons. Light signals are faster than electrical signals and produce less tissue damage.

BCBIs command robotic hands to grasp objects while tactile receptors on the robot are delivering touch and other sensory information to the user. BCBIs in development also control exoskeletal devices that reach and walk and return touch, body position, and balance information to guide movement. In essence, BCBIs use variations in CNS activity to generate signals. It is unlikely, however, that in doing so they employ the signaling codes normally used by the brain in producing behavior (Daly & Huggins, 2015).

Brain–computer–brain interfaces such as the robotic limb shown here enable the brain to command robotic devices that provide it sensory feedback.

Section 1-1 offers a simple definition of behavior: any movement in a living organism.

Movement is a defining feature of animals, and this chapter explores how the nervous system produces movement. The body senses are more closely related to movement than are the other senses. This chapter also describes how somatic sensation and movement interact at different levels of the nervous system.

At the level of the spinal cord, somatosensory information contributes to motor reflexes. In the brainstem, it contributes to movement timing and control. In the cerebrum, it contributes to complex voluntary movements. Indeed, for many functions, the other senses work through the somatosensory system to produce movement. If the motor system is a vehicle and the somatosensory system is the driver, the other sensory systems act like backseat drivers.

We begin here with movement and end with sensation. Section 4-4 begins with sensation and ends with movement.

We first consider how movement is organized in the central nervous system, then turn to how the somatic senses contribute to movement and balance. If you want to review how the motor system and somatic sensation interact before you read on, turn to The Basics: Relating the Somatosensory and Motor Systems, on pages 358–359.